The art of draining fluid from planting or bioculture media by capillary means was established in the 1949 patent of John Martin whose technique is later incorporated into the 1981 patent of Lawrence Brown. Limitations however are imposed on what exactly is drained from the container environment by the embodiments therein described, as well as on the rate at which drainage may occur. Both lift water using capillary wicks to a level above soil or culture media for the purpose of aiding the evaporation of excess water.
Martins device removes only water in the form of vapor, a slow process which requires that about 530 calories of heat energy per gram of water removed be input to the system. This slow process may allow anoxic conditions to develop to a point which may harm plants. In addition ion and colloid concentrations increase in the soil solution as does the concentration of organic matter with the removal of pure water.
Brown, who similarly uses wick means to aid the evaporation of water, adds an air pump and tubing mechanism to remove liquid as such from his culture vessels.
Neither Martin nor Brown uses capillary means to remove dissolved or suspended matter which may accumulate in considerable quantity as a result of metabolism, and neither makes use of capillary means to deliver liquid water for collection. Both use wick means solely as dispersal means for water molecules.
Green in one of several patents overcomes these difficulties by the use of sand filled pipe drains which terminate below his media and fluid supply systems thereby using capillarity, gravity, and surface tension to cause liquid to flow from the culture media. His use of sand requires a complicated special apparatus.